Tire Tread Rubber Composition

Abstract

Disclosed herein are tire tread rubber compositions comprising a specified elastomer component, reinforcing silica filler, a specified hydrocarbon resin, a cure package, and optionally oil. The elastomer component includes styrene-butadiene rubber; polybutadiene; and guayule natural rubber.

What is claimed is: 
     
         1 . A tire tread rubber composition comprising:
 a. 100 parts of an elastomer component comprising
 i. 10-50 parts of guayule natural rubber, and 
 ii. 10-60 parts of polybutadiene rubber having a cis bond content of at least 95% and a Tg of less than −101° C., 
   wherein the total amount of (i) and (ii) is at least 50 phr,   b. at least one reinforcing silica filler in an amount of 61-150 phr,   c. at least one hydrocarbon resin in an amount of 21-50 phr, wherein the resin has a Tg of about 30 to about 50° C.,   d. no more than 30 phr of oil, and   e. a cure package,   wherein the total amount of (c) and (d) is no more than 59 phr.   
     
     
         2 . The tire tread rubber composition of  claim 1 , wherein the elastomer component further comprises 20-50 parts of at least one styrene-butadiene rubber. 
     
     
         3 . The tire tread rubber composition of  claim 1 , wherein the elastomer component further comprises 20-45 parts of at least one styrene-butadiene rubber and the amount of hydrocarbon resin is no more than 45 phr. 
     
     
         4 . The tire tread rubber composition of  claim 1 , comprising no more than 20 phr of carbon black filler. 
     
     
         5 . A tire tread rubber composition comprising:
 a. 100 parts of an elastomer component comprising
 i. 20-45 parts of guayule natural rubber, 
 ii. 10-60 parts of polybutadiene rubber having a cis bond content of at least 95% and a Tg of less than −101° C., and 
 iii. 20-45 parts of at least one styrene-butadiene rubber, 
   wherein the total amount of (i) and (ii) is at least 55 phr,   b. at least one reinforcing silica filler in an amount of 81-120 phr and no more than 20 phr of carbon black filler,   c. at least one hydrocarbon resin in an amount of 21-50 phr, wherein the resin has a Tg of about 30 to about 50° C.,   d. no more than 30 phr of oil, and   e. a cure package,   wherein the total amount of (c) and (d) is no more than 59 phr.   
     
     
         6 . The tire tread rubber composition of  claim 5 , wherein the hydrocarbon resin of (c) comprises an aromatic resin. 
     
     
         7 . The tire tread rubber composition of  claim 1 , wherein the average Tg of the elastomer component is about −75 to about −90° C. 
     
     
         8 . The tire tread rubber composition of  claim 5 , wherein the hydrocarbon resin of (c) contains less than 40% by weight aliphatic C5 monomer, and includes less than 5 phr of terpene resin. 
     
     
         9 . A tire tread rubber composition comprising:
 a. 100 parts of an elastomer component comprising
 i. 20-45 parts of guayule natural rubber, 
 ii. 10-60 parts of polybutadiene rubber having a cis bond content of at least 95% and a Tg of less than −101° C., and 
 iii. 20-45 parts of at least one styrene-butadiene rubber, 
   wherein the total amount of (i) and (ii) is at least 55 phr and the average Tg of the elastomer component is about −75 to about −90° C.,   b. at least one reinforcing silica filler in an amount of 81-120 phr and no more than 20 phr of carbon black filler,   c. at least one aromatic hydrocarbon resin in an amount of 21-50 phr, wherein the resin has a Tg of about 30 to about 50° C.,   d. no more than 30 phr of oil, and   e. a cure package,   wherein the total amount of (c) and (d) is no more than 59 phr.   
     
     
         10 . The tire tread rubber composition of  claim 9 , wherein the hydrocarbon resin of (c) includes less than 5 phr of terpene resin. 
     
     
         11 . The tire tread rubber composition of  claim 9 , wherein the hydrocarbon resin of (c) contains less than 50% by weight aliphatic C5 monomer. 
     
     
         12 . The tire tread rubber composition of  claim 1 , wherein the hydrocarbon resin of (c):
 comprises a vinyl aromatic homopolymer or copolymer resin,   contains less than 40% by weight aliphatic C5 monomer, and   includes less than 5 phr of terpene resin.   
     
     
         13 . The tire tread rubber composition of  claim 9 , wherein the hydrocarbon resin of (c) comprises a vinyl aromatic homopolymer or copolymer resin. 
     
     
         14 . The tire tread rubber composition of  claim 1 , wherein the elastomer component comprises less than 20 parts of emulsion styrene-butadiene rubber. 
     
     
         15 . The tire tread rubber composition of  claim 1 , wherein any oil present contains 50% by weight or less oleic acid. 
     
     
         16 . The tire tread rubber composition of  claim 1 , wherein the at least one reinforcing silica filler has a surface area of 170 to 300 m 2 /g. 
     
     
         17 . The tire tread rubber composition of  claim 1 , wherein the rubber composition has a value for tan δ at 60° C. of 0.18 to 0.25 and meets at least one of the following
 a. has a value for tan δ at −30° C. of at least 2 times the tan δ at 60° C. value; 
 b. has a value for tan δ at 0° C. of at least 1.5 times the tan δ at 60° C. value; or 
 c. has a value for tan δ at 30° C. of at least 1.1 times the tan δ at 60° C. value. 
 
     
     
         18 . The tire tread rubber composition of  claim 5 , wherein the rubber composition has a value for tan δ at 60° C. of 0.18 to 0.25 and meets at least one of the following
 a. has a value for tan δ at −30° C. of at least 2 times the tan δ at 60° C. value; 
 b. has a value for tan δ at 0° C. of at least 1.5 times the tan δ at 60° C. value; or 
 c. has a value for tan δ at 30° C. of at least 1.1 times the tan δ at 60° C. value. 
 
     
     
         19 . The tire tread rubber composition of  claim 17 , wherein each of (a), (b), and (c) are met. 
     
     
         20 . A tire including a tread comprising the tire tread rubber composition of  claim 1 .